1 /*
2 * Copyright (c) 2001, 2016, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "gc/g1/concurrentMarkThread.inline.hpp"
28 #include "gc/g1/g1Analytics.hpp"
29 #include "gc/g1/g1CollectedHeap.inline.hpp"
30 #include "gc/g1/g1CollectorPolicy.hpp"
31 #include "gc/g1/g1MMUTracker.hpp"
32 #include "gc/g1/suspendibleThreadSet.hpp"
33 #include "gc/g1/vm_operations_g1.hpp"
34 #include "gc/shared/gcId.hpp"
35 #include "gc/shared/gcTrace.hpp"
36 #include "gc/shared/gcTraceTime.inline.hpp"
37 #include "logging/log.hpp"
38 #include "memory/resourceArea.hpp"
39 #include "runtime/vmThread.hpp"
40
41 // ======= Concurrent Mark Thread ========
42
43 // The CM thread is created when the G1 garbage collector is used
44
45 ConcurrentMarkThread::ConcurrentMarkThread(G1ConcurrentMark* cm) :
46 ConcurrentGCThread(),
47 _cm(cm),
48 _state(Idle),
49 _vtime_accum(0.0),
50 _vtime_mark_accum(0.0) {
51
52 set_name("G1 Main Marker");
53 create_and_start();
54 }
55
56 class CMCheckpointRootsFinalClosure: public VoidClosure {
57
58 G1ConcurrentMark* _cm;
59 public:
60
61 CMCheckpointRootsFinalClosure(G1ConcurrentMark* cm) :
62 _cm(cm) {}
63
64 void do_void(){
65 _cm->checkpointRootsFinal(false); // !clear_all_soft_refs
66 }
67 };
68
69 class CMCleanUp: public VoidClosure {
70 G1ConcurrentMark* _cm;
71 public:
72
73 CMCleanUp(G1ConcurrentMark* cm) :
74 _cm(cm) {}
75
76 void do_void(){
77 _cm->cleanup();
78 }
79 };
80
81 // Marking pauses can be scheduled flexibly, so we might delay marking to meet MMU.
82 void ConcurrentMarkThread::delay_to_keep_mmu(G1CollectorPolicy* g1_policy, bool remark) {
83 const G1Analytics* analytics = g1_policy->analytics();
84 if (g1_policy->adaptive_young_list_length()) {
85 double now = os::elapsedTime();
86 double prediction_ms = remark ? analytics->predict_remark_time_ms()
87 : analytics->predict_cleanup_time_ms();
88 G1MMUTracker *mmu_tracker = g1_policy->mmu_tracker();
89 jlong sleep_time_ms = mmu_tracker->when_ms(now, prediction_ms);
90 os::sleep(this, sleep_time_ms, false);
91 }
92 }
93
94 class G1ConcPhaseTimer : public GCTraceConcTimeImpl<LogLevel::Info, LOG_TAGS(gc, marking)> {
95 G1ConcurrentMark* _cm;
96
97 public:
98 G1ConcPhaseTimer(G1ConcurrentMark* cm, const char* title) :
99 GCTraceConcTimeImpl<LogLevel::Info, LogTag::_gc, LogTag::_marking>(title),
100 _cm(cm) {
101 _cm->gc_timer_cm()->register_gc_concurrent_start(title);
102 }
103
104 ~G1ConcPhaseTimer() {
105 _cm->gc_timer_cm()->register_gc_concurrent_end();
106 }
107 };
108
109 void ConcurrentMarkThread::run_service() {
110 _vtime_start = os::elapsedVTime();
111
112 G1CollectedHeap* g1h = G1CollectedHeap::heap();
113 G1CollectorPolicy* g1_policy = g1h->g1_policy();
114
115 while (!should_terminate()) {
116 // wait until started is set.
117 sleepBeforeNextCycle();
118 if (should_terminate()) {
119 break;
120 }
121
122 GCIdMark gc_id_mark;
123
124 cm()->concurrent_cycle_start();
125
126 assert(GCId::current() != GCId::undefined(), "GC id should have been set up by the initial mark GC.");
127
128 GCTraceConcTime(Info, gc) tt("Concurrent Cycle");
129 {
130 ResourceMark rm;
131 HandleMark hm;
132 double cycle_start = os::elapsedVTime();
133
134 {
135 G1ConcPhaseTimer t(_cm, "Concurrent Clear Claimed Marks");
136 ClassLoaderDataGraph::clear_claimed_marks();
137 }
138
139 // We have to ensure that we finish scanning the root regions
140 // before the next GC takes place. To ensure this we have to
141 // make sure that we do not join the STS until the root regions
142 // have been scanned. If we did then it's possible that a
143 // subsequent GC could block us from joining the STS and proceed
144 // without the root regions have been scanned which would be a
145 // correctness issue.
146
147 {
148 G1ConcPhaseTimer t(_cm, "Concurrent Scan Root Regions");
149 _cm->scan_root_regions();
150 }
151
152 // It would be nice to use the GCTraceConcTime class here but
153 // the "end" logging is inside the loop and not at the end of
154 // a scope. Mimicking the same log output as GCTraceConcTime instead.
155 jlong mark_start = os::elapsed_counter();
156 log_info(gc, marking)("Concurrent Mark (%.3fs)", TimeHelper::counter_to_seconds(mark_start));
157
158 int iter = 0;
159 do {
160 iter++;
161 if (!cm()->has_aborted()) {
162 G1ConcPhaseTimer t(_cm, "Concurrent Mark From Roots");
163 _cm->mark_from_roots();
164 }
165
166 double mark_end_time = os::elapsedVTime();
167 jlong mark_end = os::elapsed_counter();
168 _vtime_mark_accum += (mark_end_time - cycle_start);
169 if (!cm()->has_aborted()) {
170 delay_to_keep_mmu(g1_policy, true /* remark */);
171 log_info(gc, marking)("Concurrent Mark (%.3fs, %.3fs) %.3fms",
172 TimeHelper::counter_to_seconds(mark_start),
173 TimeHelper::counter_to_seconds(mark_end),
174 TimeHelper::counter_to_millis(mark_end - mark_start));
175
176 CMCheckpointRootsFinalClosure final_cl(_cm);
177 VM_CGC_Operation op(&final_cl, "Pause Remark", true /* needs_pll */);
178 VMThread::execute(&op);
179 }
180 if (cm()->restart_for_overflow()) {
181 log_debug(gc, marking)("Restarting Concurrent Marking because of Mark Stack Overflow in Remark (Iteration #%d).", iter);
182 log_info(gc, marking)("Concurrent Mark Restart due to overflow");
183 }
184 } while (cm()->restart_for_overflow());
185
186 if (!cm()->has_aborted()) {
187 G1ConcPhaseTimer t(_cm, "Concurrent Create Live Data");
188 cm()->create_live_data();
189 }
190
191 double end_time = os::elapsedVTime();
192 // Update the total virtual time before doing this, since it will try
193 // to measure it to get the vtime for this marking. We purposely
194 // neglect the presumably-short "completeCleanup" phase here.
195 _vtime_accum = (end_time - _vtime_start);
196
197 if (!cm()->has_aborted()) {
198 delay_to_keep_mmu(g1_policy, false /* cleanup */);
199
200 CMCleanUp cl_cl(_cm);
201 VM_CGC_Operation op(&cl_cl, "Pause Cleanup", false /* needs_pll */);
202 VMThread::execute(&op);
203 } else {
204 // We don't want to update the marking status if a GC pause
205 // is already underway.
206 SuspendibleThreadSetJoiner sts_join;
207 g1h->collector_state()->set_mark_in_progress(false);
208 }
209
210 // Check if cleanup set the free_regions_coming flag. If it
211 // hasn't, we can just skip the next step.
212 if (g1h->free_regions_coming()) {
213 // The following will finish freeing up any regions that we
214 // found to be empty during cleanup. We'll do this part
215 // without joining the suspendible set. If an evacuation pause
216 // takes place, then we would carry on freeing regions in
217 // case they are needed by the pause. If a Full GC takes
218 // place, it would wait for us to process the regions
219 // reclaimed by cleanup.
220
221 G1ConcPhaseTimer t(_cm, "Concurrent Complete Cleanup");
222 // Now do the concurrent cleanup operation.
223 _cm->complete_cleanup();
224
225 // Notify anyone who's waiting that there are no more free
226 // regions coming. We have to do this before we join the STS
227 // (in fact, we should not attempt to join the STS in the
228 // interval between finishing the cleanup pause and clearing
229 // the free_regions_coming flag) otherwise we might deadlock:
230 // a GC worker could be blocked waiting for the notification
231 // whereas this thread will be blocked for the pause to finish
232 // while it's trying to join the STS, which is conditional on
233 // the GC workers finishing.
234 g1h->reset_free_regions_coming();
235 }
236 guarantee(cm()->cleanup_list_is_empty(),
237 "at this point there should be no regions on the cleanup list");
238
239 // There is a tricky race before recording that the concurrent
240 // cleanup has completed and a potential Full GC starting around
241 // the same time. We want to make sure that the Full GC calls
242 // abort() on concurrent mark after
243 // record_concurrent_mark_cleanup_completed(), since abort() is
244 // the method that will reset the concurrent mark state. If we
245 // end up calling record_concurrent_mark_cleanup_completed()
246 // after abort() then we might incorrectly undo some of the work
247 // abort() did. Checking the has_aborted() flag after joining
248 // the STS allows the correct ordering of the two methods. There
249 // are two scenarios:
250 //
251 // a) If we reach here before the Full GC, the fact that we have
252 // joined the STS means that the Full GC cannot start until we
253 // leave the STS, so record_concurrent_mark_cleanup_completed()
254 // will complete before abort() is called.
255 //
256 // b) If we reach here during the Full GC, we'll be held up from
257 // joining the STS until the Full GC is done, which means that
258 // abort() will have completed and has_aborted() will return
259 // true to prevent us from calling
260 // record_concurrent_mark_cleanup_completed() (and, in fact, it's
261 // not needed any more as the concurrent mark state has been
262 // already reset).
263 {
264 SuspendibleThreadSetJoiner sts_join;
265 if (!cm()->has_aborted()) {
266 g1_policy->record_concurrent_mark_cleanup_completed();
267 } else {
268 log_info(gc, marking)("Concurrent Mark Abort");
269 }
270 }
271
272 // We now want to allow clearing of the marking bitmap to be
273 // suspended by a collection pause.
274 // We may have aborted just before the remark. Do not bother clearing the
275 // bitmap then, as it has been done during mark abort.
276 if (!cm()->has_aborted()) {
277 G1ConcPhaseTimer t(_cm, "Concurrent Cleanup for Next Mark");
278 _cm->cleanup_for_next_mark();
279 } else {
280 assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear");
281 }
282 }
283
284 // Update the number of full collections that have been
285 // completed. This will also notify the FullGCCount_lock in case a
286 // Java thread is waiting for a full GC to happen (e.g., it
287 // called System.gc() with +ExplicitGCInvokesConcurrent).
288 {
289 SuspendibleThreadSetJoiner sts_join;
290 g1h->increment_old_marking_cycles_completed(true /* concurrent */);
291
292 cm()->concurrent_cycle_end();
293 }
294 }
295 _cm->root_regions()->cancel_scan();
296 }
297
298 void ConcurrentMarkThread::stop_service() {
299 MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag);
300 CGC_lock->notify_all();
301 }
302
303 void ConcurrentMarkThread::sleepBeforeNextCycle() {
304 // We join here because we don't want to do the "shouldConcurrentMark()"
305 // below while the world is otherwise stopped.
306 assert(!in_progress(), "should have been cleared");
307
308 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
309 while (!started() && !should_terminate()) {
310 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
311 }
312
313 if (started()) {
314 set_in_progress();
315 }
316 }